1. Field of the Invention
This invention relates to an improved process for the alkylation of aromatic substrates. In particular, it relates to a process using selected metal cation salts of perfluorosulfonic acid polymers as alkylation catalysts.
2. Background
The catalytic alkylation of aromatic substrates is well known in the art and cannot be discussed in detail in this specification. The following limited number of publications provides adequate background for an understanding of the invention herein.
Research Disclosure, July (1980), p. 270-271, summarizes the known catalytic uses, including the alkylation of aromatic hydrocarbons, of polymers containing perfluorosulfonic acid groups.
Olah et al., J. Org. Chem. 42, p. 4187-4191 (1977), disclose the use of perfluorosulfonic acid polymers as ethylation catalysts for benzene; the thermal stability of the catalyst rapidly decreases at about 220.degree. C.
Olah et al., J. Org. Chem. 47, p. 596-598 (1982), disclose the use of a mercury (II)-impregnated perfluorosulfonic acid polymer in nitration of aromatics with nitric acid, and Olah et al., Synthesis, p. 671-672 (September, 1978), disclose the use of a mercury (II)-impregnated perfluorosulfonic acid polymer as an alkyne hydration catalyst.
U.S. Pat. Nos. 4,022,847 and 4,041,090 disclose that, in the alkylation of benzene to ethylbenzene using a perfluorosulfonic acid polymer as catalyst, the reaction temperature must be kept below about 225.degree. C. due to the lack of stability of the catalyst at temperatures above 250.degree. C.
U.S. Pat. Nos. 4,038,213 and 4,060,565 disclose the use of a supported perfluorosulfonic acid polymer as a catalyst for the alkylation of benzene. The temperature must be kept below about 205.degree. C. to avoid serious catalyst deactivation, as judged by decreased olefin conversion.
Krespan, J. Org. Chem. 44, p. 4924-4929 (1979), discloses the alkylation of selected aromatic substrates using a perfluorosulfonic acid polymer catalyst.
U.S. Pat. No. 4,356,318 discloses the use of Group VIII metal cations of perfluorosulfonic acid polymers as catalysts for the oxidative carbonylation of toluene to toluic acid.
Grot, Research Disclosure, (August) 1982, p. 280, discloses the preparation of cation salts of perfluorosulfonic acid polymers with such metals as nickel, palladium, and platinum. The metal salts are reduced to the metal, and the product may be used as a catalyst.
Kamm, Research Disclosure, (August) 1982, p. 280-281, discloses the conversion of sulfonic acid groups of a polymeric perfluorosulfonic acid to the sulfonate salt of a catalytically active metal.
Peluso, Research Disclosure, (September) 1982, p. 311, discloses porous supported catalysts prepared from perfluorosulfonic acid polymers and metal ions such as transition metal ions, for example, palladium.
Peluso, Dissertation Abstracts International 41, p. 4536B-4537B (June 1981), discloses the reaction of Cu.sup.+2 and Pd(II) perfluorosulfonic acid ionomers with carbon monoxide and nitric oxide, and the Pd(II) ionomer with ethylene.
Kelly et al., Du Pont Innovation 4, (No. 2), p. 4-7 (1973), disclose the use of Nafion.RTM. perfluorosulfonic acid copolymer membranes as cation exchange membranes in Donnan dialysis.
Du Pont Nafion.RTM. perfluorosulfonic acid product bulletin, February 1976, Table 1, discloses water absorbtion of the cation form of the Nafion.RTM. membrane with a number of cations.
Alkylation of aromatic substrates in the presence of a Lewis acid catalyst is well-known, and this general reaction is reviewed by Olah in Part II of "Friedel-Crafts and Related Reactions," Interscience Publishers (1964). More recently, as is evident from the aforesaid publications, it has been discovered that a perfluorosulfonic acid polymer can be employed as the Lewis acid catalyst. The use of such a catalyst avoids the corrosiveness of the commercially important catalyst systems based on aluminum chloride and aluminum chloride/hydrochloric acid. However, the catalyst systems based on a perfluorosulfonic acid polymer appear to have a maximum useful operating temperature of about 225.degree. C. Above that temperature the catalyst lacks thermal stability, and the yields and conversions of the products and starting materials, respectively, are decreased.
It is an object of this invention to provide an improved process for the alkylation of aromatic substrates. Another object is to provide such a process which avoids the corrosive environment which is normally associated with aluminum chloride-based catalyst systems. Still another object is to provide such a process which employs a type of perfluorosulfonic acid polymer catalyst system which is operable at much higher temperatures than the perfluorosulfonic acid polymer systems currently known in the art. These and other objects will be apparent from the following description of the invention.